The present invention relates to improvements in fluid-flow mechanisms which promote laminar-flow conditions, and, in one particular aspect, to novel and advantageous compact cartridge-type flow regulators of precision yet economical construction which are distinctively adapted for insertion into and withdrawal from the main flow path of a flowmeter having a sensor in shunt relationship, for measurement-range control and for occasional purging.
Volumetric and mass flowmetering equipment has evolved into a wide variety of forms and sizes, applying numerous different principles of operation, and functioning to accommodate fluent materials whose densities, flow rates, viscosities and compositions may be quite dissimilar. Among these are classes of sensitive and rapid-response accurate flowmeters of the so-called "hot wire" type, which are particularly useful in respect of measurements of gaseous-fluid flow, and which exploit the phenomenon that a flowing fluid encountering a mass at a higher temperature tends to cool it to an extent which at least in part depends upon the rate of flow. For example, it has been known to introduce an electrical heater into a stream, and to maintain its supply of electrical power essentially constant while interpreting the differences between upstream and downstream temperatures as measurements of flow; similarly, mass flow has been metered by determining the temperature differentials between temperature-sensitive heating coils which are in upstream and downstream relations to the flowing fluid and which are elements of electrical bridge circuitry serving both measuring and heating purposes. Accurate measurements are obtainable in the latter types of flowmeters only if essentially laminar flow conditions are preserved, and it has therefore been a common practice to conduct the bypass flow through a rather highly elongated slender sensor tube and to exchange heat with the flowing fluid externally through thin walls of the tube without interposing obstructions internally (U.S. Pat. Nos. 3,433,068 and 3,613,448 and 3,851,526 and 3,938,384). The bypass of flow-splitting technique allows one such sensor tube, with its associated heaters and temperature detectors, to develop reliable measurements over a multitude of flow ranges, provided the main flow path which it shunts is also one in which laminar flow conditions are preserved, regardless of the extent to which flow is restricted in that main path. Because laminar flow conditions do not obtain unless each constricted flow path has an effective length-to-diameter ratio of at least about one hundred, the range-governing restrictors employed in the main flow path would be of inconvenient lengths unless their flow openings were convoluted into short spans (as in said U.S. Pat. No. 3,851,526) or were fashioned into minute-diameter channels; however, both such practices invite unwanted manufacturing difficulties and expense.